2015-11-18

Abstract :

The interplay between charge and spin currents at the interface between paramagnetic metals and ferromagnetic insulators results in novel spintronic effects, such as the recently discovered spin-Hall magnetoresistance (SMR). It commonly manifests itself in an unexpected dependence of the resistivity of a paramagnetic Pt layer (representing the most widely used spin-Hall material) on the magnetization of an adjacent ferrimagnetic insulator, such as Y3Fe5O12 or NiFe2O4 [1,2]. While different groups agree in this experimental observation [1,2,3], its interpretation is still a matter of debate and far from being settled. Two conflicting models are discussed. One relies on the reflection or absorption of spin currents at the Pt/Y3Fe5O12 interface [1,2,4], the second proposes a static magnetic proximity effect in Pt [3].

I here discuss our latest results on the magnetic proximity effect, the SMR effect, and the spin-Hall anomalous Hall effect (SH-AHE) in the Pt/Y3Fe5O12 system from a comprehensive investigation of different samples as a function of the thickness t of the Pt layer. We identify a maximum of the SMR at room temperature for t = 3 nm with a decrease towards smaller t or lower temperatures [5]. We further find a maximum of the SH-AHE also for t = 3 nm, again with a decrease towards smaller t [6]. These observations are fully consistent with the prediction of the SMR theory [4] and cannot be attributed to a magnetic proximity effect. Finally, we study the X-ray absorption spectra (XAS) and the X-ray magnetic circular dichroism (XMCD) at the Pt L2,3 edges. The normalized XAS whiteline intensity in all samples is lower than 1.30, evidencing a clean metallic Pt layer. The XMCD is close to zero, showing that the induced magnetic moment in Pt is negligibly small (< 0.003 µB per Pt atom), even down to t = 1.6 nm [7]. In summary, our data are fully consistent with the SMR model [4]. We do not find indication for a static magnetic proximity effect in Pt on Y3Fe5O12.

Acknowledgments:
This work is supported by the European Synchrotron Radiation Facility (ESRF) via HE-3784, HC-1500, and HC-2058, as well as by the Deutsche Forschungsgemeinschaft (DFG) via SPP 1538.